Effects of BaO, CaO and V2O5 additions on the solubility of SO42- and Cl- in silicate and borosilicate glasses

Effects of BaO, CaO and V2O5 additions on the solubility of SO42- and Cl- in silicate and borosilicate glasses

Shuchi Vaishnav <Shuchi.Vaishnav@student.shu.ac.uk>

Currently enrolled as a Postdoctoral Research Associate at the Materials and Engineering Research Institute (MERI) at Sheffield Hallam University, UK. My PhD research topic dealt with enhancement of silicate and borosilicate glass systems used for radioactive waste immobilization, with focus on high level wastes containing high levels of sulphate ions. My research interests include structural characterisation of glasses using various spectroscopic techniques including Raman spectroscopy, MAS-NMR, XRD, Neutron Diffraction, XANES and EXAFS. I was previously employed as a nuclear reactor researcher at EDF R&D, France; IGCAR-India; and the IPR-Fusion ITER unit, India/France.

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Some radioactive wastes generated at multiple U.S. defence and commercial nuclear facilities contain high concentrations of Cl– and SO42- ions, which arise through various reprocessing routes. The poor solubility of these ions in borosilicate waste glasses has limited waste loadings and increased waste volumes, with logistical and economic repercussions on the waste vitrification industry. Enhanced capacities to incorporate (i) SO42- with addition of Ba2+ and V5+ in borosilicate glasses; and (ii) Cl– with addition of Ca2+ in silicate glasses, have been investigated previously, however, the resulting glasses were not structurally analysed in depth. In the present study, a set of simple ternary silicate and borosilicate glasses, Na2O-RO-SiO2 and Na2O-RO-B2O3-SiO2 (R=Ba, Ca), were developed and doped excessively with sulphate and chloride ions, respectively. Additionally, two series of SO42-and Cl– doped simulant U.S. HLW waste glasses were prepared with pro-rata addition of V2O5. The final glass compositions were analysed using XRF, ICP and EDS. Structural characterisation was carried out using techniques including Raman spectroscopy, MAS-NMR, neutron diffraction and S K-edge XANES. Preliminary results of the compositional and structural analyses of these glasses will be presented here, providing useful insight into understanding the solubility-determining factors of the anions in more complex industrial radioactive waste glasses.